1941-1942: Canadian firm Ayerst, McKenna and Harrison introduces Premarin, a combination of estrogens produced from the urine of pregnant mares, the most potent form of the hormone yet developed.
(COURTESY OF SCHERING-PLOUGH)

1951: After six years of prescribing estrogen to institutionalized elderly patients, sex researcher William Masters recommends hormone therapy to rejuvenate “mental and physical function.”

1953: Mayo Clinic scientists posit that estrogen is cardioprotective after performing autopsies and finding that women who had their ovaries removed suffered more advanced atherosclerosis than women with ovaries.

2002: The estrogen-plus-progestin arm of the 27,000-subject Women’s Health Initiative study is halted three years early when it substantiates increased risk of breast cancer, heart attacks, strokes and blood clots.

2004: The Premarin arm of the WHI study is ended a year ahead of schedule because estrogen alone offered no cardioprotective benefit but increased the risk of blood clots and stroke.
(SCOTT CAMAZINE/PHOTOTAKE)

2005-PRESENT: Hormone therapy is recommended only for relief of severe menopausal symptoms and for the shortest time possible.
( PAUL BURNS/DIGITAL VISION/GETTY IMAGES)